Heating of fluid



Nov. 10, 1935.- NELSON 2,060,338

HEATING 'OF FLUIDS Filed Oct. 23, 1953 TF FRACTIONATOR 1* CONDEN SER 63,

INVENTOR EDWIN F; ELSON AT NEY the air required for combustion through the centralor combustion duct I I of firing tunnel 9 to combustionand heating zone 6 and additional air for combustion may be supplied through ducts I2 located above and beneath duct l I and controlled by dampers I3.

In the case illustrated, a single horizontal row or bank I4 of horizontally disposed tubes I5 is disposed adjacent the floor 4 of the furnace beneath. firing tunnel 9. Adjacent tubes of this bank are connected at their ends in series by means of headers or return bends of any well known form (not shown), the connections between the tubes at their near ends being indicated. however, by lines I6. Tube bank I4 is supplied, primarily, with radiant heat from the combustion gases in combustion and heating zone 6 and from the hot refractory walls of the furnace and, due to its position in the furnace, a relatively high rate of heating is obtained in this portion of the fluid conduit. It will be understood that more than one row of tubes may be employed adjacent the floor of the furnace, although only one is illustrated in the drawing, but preferably not more than three such rows are employed for the heating of relatively high boiling hydrocarbon oils, in order that a high radiant heat input may be obtained and the oil quickly brought to the desired conversion temperature.

A plurality of horizontal rows of horizontally disposed tubes I'I, comprising bank I8, is located within heating zone 1, adjacent tubes in each row and adjacent rows of tubes being connected in series, as indicated by the connecting lines I9 at the near end of the tubes, headers or return bends of any well known type (not shown) being employed for this purpose.

Another tube bank 20 comprising, in the case illustrated, a single horizontal row of horizontally disposed tubes 2I, connected at their ends in series, as indicated by lines 22 at the near ends of the tubes,.is disposed adjacent the roof 3 of the furnace. Suitable headers or return bends (not shown) are also employed for connecting the ends of adjacent tubes in bank 20. It will be understood that although the drawing illustrates only a single row of tubes in bank 20, more than one row of tubes disposed adjacent the roof of the furnace may be employed, when desired.

Tube banks I8 and 20 comprise, in the case illustrated, that portion of the fluid conduit through which the relatively low boiling oil is passed. Tube bank 20 receives radiant heat from the combustion gases and hot refractory walls of the furnace as well as convection heat from the furnace gases passing over the tubes and, normally, somewhat lower rates of heating are obtained in bank 20 as compared with those obtained in bank I4. Still lower rates of heating are obtained in tube bank I8. which is supplied with both radiant and convection heat (primarily the latter) from the furnace gases passing through this zone of the furnace. Although the temperature of the products emerging from the light oil heating coil is preferably higher than the final oil temperature obtained in the heavy oil heating coil 9. more gradual rate of heating and more prolonged conversion time is obtainr d in the light oil coil.

The invention, as employed in the specific type of furnace illustrated and described, is not limited to any particular path or direction of flow through the various tubes or tube banks of the fluid conduits except that low boiling oil is passed through tube banks I8 and 20 and high boiling oil through tube bank I4. In the case here illustrated, the

low boiling oil enters the bottom row of tubes in tube bank I8, passing upward through succeeding rows of this bank in a general direction countercurrent to the flow of combustion gases through this zone, passing from the last tube in the top row of this bank to the tube of bank 20 adjacent end wall 2 of the furnace and through successive adjacent tubes in this bank, finally emerging from the tube adjacent end wall I of the furnace. The high boiling oil enters the tube of bank I4 nearest bridge wall 5, passing through adjacent tubes in this row in series and emerging from the tube at the opposite end of this bank most adjacent end wall I of the furnace.

Referring now to the entire cracking apparatus illustrated in the drawing, raw oil charging stock for the process is supplied through line 3I and valve 32 to pump 33 from which it is fed through line 34 and may pass, all or in part, either through line 35 and valve 36 into fractionator 31 or through line 38 and valve 39 into the light oil heating coil comprising tube banks I8 and 20 or from line 38 through line 40 and valve 4| into the heavy oil heating coil comprising tube bank I4. The method of supplying the charging stock to the system will, of course. depend upon its nature; being supplied to banks I8 and 20 when it is of relatively low boiling nature and to bank I4 when it is of relatively high boiling nature or, in either case, the charging stock may be supplied to fractionator 31, when desired, except in case it contains low boiling components which would contaminate the overhead stream of vaporous products removed from fractionator 31 and comprising the final light distillate product of the process. When the charging stock is of relatively wide boiling range, containing materials which it is desirable to convert in both the light oil and heavy oil coils, it is preferably supplied to fractionator 31 wherein it may be separated into low boiling and high boiling f1 actions. together with the reflux condensate removed from the vaporous products undergoing fractionation in this zone, the low boiling fractions being supplied to the light oil heating coil and the high boiling fractions to the heavy oil heating coil.

The high boiling oil, after being quickly heated to the desired conversion temperature in tube bank I4,'is discharged therefrom, in the case illustrated. through'line 42, valve 43 and line 44 into reaction chamber 46, while the low boiling oil, after being subjected to more prolonged conversion temperature, through line 44 and valve 45 also into reaction-chamber 48.

Substantial superatmospheric pressure is preferably employed in both the light oiland the heavy oil heating coils, higher pressure being preferred in the light oil heating coil. than that employed in the heavy oil coil, and the pressure employed in the reaction chamber may be substantially the same as that employed in the heavy oil heating coil or may be substantially reduced relative thereto.

Vaporous and liquid conversion products separate in chamber 48." The latter may be withdrawn from the lower portion of the chamber through line 41 and valve 48 to cooling and storage or to any desired further treatment or, when desired, operating conditions of the process may be so controlled that only substantially dry coke is produced as the residual product of the process. in which case this material may be allowed to accumulate in chamber 46 to be removed therefrom, in any well known manner not shown) after the operation of the chamber is completed.

When desired, a plurality of coking chambers, similar to chamber 46, but not illustrated in the drawing, may be employed and may be operated either alternately or simultaneously.

Vaporous conversion products pass from the upper portion of chamber through line 49 and valve 50 to fractionation in fractionator 31. The insufilciently converted components of the vapors, boiling above the range of the desired final light distillate product of the process, are condensed in fractionator 37 as reflux condensate and, in the case here illustrated, the reflux condensate is separated into low boiling and high boiling fractions.

The high boiling fractions of the reflux condensate are withdrawn from the lower portion'of the fractionator through line 5| and valve 52 to pump 53, by means of which they are returned through line 54, valve 55 and line 50 to the heavy oil heating coil.

Low boiling fractions of the reflux condensate are removed from one or a plurality of suitable intermediate points in the fractionator passing, for example, through line 56 and valve 5! to pump 58, by means of which they are returned through line 59, valve 60 and line 38 to the light oil heating coil.

Fractionated vapors of the desired end boiling point, preferably comprising materials within the boiling range of motor fuel and of good antiknock value, are withdrawn from the upper portion of fractionator 31 through line 6| and valve 62 and are subjected to condensation and cooling in condenser .63. The resulting distillate and gas passes through line 64 and valve 65 to collection and separation in receiver 66. Uncondensable gas may be released from the receiver through line 61 and valve 68. Distillate may be withdrawn from receiver 66 through line 69 and valve 16 to storage or to any desired further treatment. When desired, a regulated portion of the distillate collecting in receiver 66 may be returned, by well known means (not shown), to the upper portion In an apparatus such as illustrated, the operating conditions of the process described may be approximately as follows: an average heat transfer rate ranging from approximately 5.500

'to 8,500 B. t. u.s per square foot, per hour may be employed in the light oil heating coil and the conversion temperature employed at the outlet from this zone may range, for example, from 925 to 1050 F., or thereabouts, preferably with a superatmospheric pressure of from 200 to 800 pounds, or more, per square inch, at this point in the system. A higher heat transfer rate of the order '0: 12,000 to 15,000 B. t. u.s per square foot per hour is preferably employed in the heavy oil heating coil with a minimum velocity in' this zone. based upon the volume of relatively cold oil entering the coil and neglecting the increased velocity due 'to expansion and v vaporization upon heating, of approximately 7 to 8 per feet per second. The conversion temperature employed at the outlet from the heavy oil heating coil may range, for example, from 800 to 950 F., or thereabouts, and preferably a superatmospheric pressure of from 100 to 500 pounds, or thereabouts, persquare inch is employed at this point in the system. Any desired pressure ranging from substantially atmospheric to a superatmospheric pressure of the order of 500 pounds, or thereabouts, -per square inch may be employed in the reaction chamber, the pressure in this zonebeing, however, no greater than that employed at the outlet from the heating coil employing the lowest pressure. The pressure employed in the reaction chamber may be either substantially equilized or somewhat reduced in the succeeding fractionating, condensing and collecting portions of the cracking system.

As an example of the improved operation of a cracking process, such as illustrated and above described, utilizing the features of the present invention, as compared with a similar operation utilizing separate furnaces for heating the light and heavy oils and employing only high rates of heating in the furnace devoted to heating the heavy oil, the single furnace of the present invention may have an overall thermal efliciency of the order of 65 to 70% as compared with an efliciency of approximately 50%, for example,

receiving combustion gases from the radiant i section, and the furnace fired adjacent the lower portion of the radiant heat section} the method which comprises passing a stream of relatively heavy oil at high velocity through a fluid conduit adjacent the floor of said radiant section and subjecting the same therein to high rates of heating for a short period of time, and simul-J 

